Titanosilicate is a novel heteroatom molecular sieve developed from the early 1980s. The synthesized titanosilicate molecular sieves currently include TS-1 having the MFI-type structure, TS-2 having the MEL-type structure, Ti-MCM-22 having the MWW-type structure and TS-48 having a relatively greater pore structure. Among said titanosilicate molecular sieves, the titanosilicate TS-1 developed by Enichem, Italy, is a novel titanosilicate having excellent catalytic selectivity and oxidation property and formed by introducing a transition metal, titanium, into the molecular sieve framework having a ZSM-5 structure. TS-1 has not only the catalytic oxidation of titanium, but also the shape-selective function and excellent stability of ZSM-5 molecular sieves. The titanosilicate material as a catalyst can be used to catalyze various organic oxidations, such as epoxidation of olefins, partial oxidation of alkanes, oxidation of alcohols, hydroxylation of phenols, ammoxidation of cyclones and the like. In the oxidation of organic substances using TS-1 molecular sieves, hydrogen peroxide which is pollution free and in a low concentration may be used as an oxidizing agent, so as to avoid the complex technology and environmental pollution in the oxidation process. It also has the advantages of energy conservation, economization, environmental benign incomparable by the conventional oxidation system, and has better reaction selectivity. Thus it has a great industrial application prospect. The titanosilicate as a catalyst for selective oxidation of organic substances is deemed to a milestone in the field of molecular sieve catalysis.
H2O2 is a well-acknowledged green oxidizing agent, and the by-product of oxidation merely includes water. However, the aqueous solution of H2O2 is difficult to be stored and transported. H2O2 is extremely unstable and will be decomposed when being in contact with heat, light, rough surface, heavy metals and other impurities. Moreover, special safety measures shall be taken during the packaging, storage and transportation due to the corrosivity thereof. Thus such chemical product can be effectively used only if H2O2 is used on-site, or the production process of H2O2 is combined with the downstream process in which H2O2 is used.
H2O2 can be directly synthesized by using H2 and O2, and the atom utilization rate reaches 100%. Thus people hope to use H2 and O2 to in situ synthesize H2O2 and then oxidize the organic material, so as to solve the cost and safety problems induced by directly using H2O2. Since Pt, Pd, Au and so on are the effective components for synthesizing H2O2 by using H2 and O2, many patent documents reported the studies on supporting them on the titanosilicate material to in situ produce H2O2 for the selective oxidation of organic substances. For example, Meiers R. et al (J. Catal., 1998, 176:376-386) made studies on the propylene gas phase epoxidation by using Pt—Pd/TS-1 as the catalyst. In addition, U.S. Pat. No. 6,867,312B1 and U.S. Pat. No. 6,884,898B1 also made such studies. Although said technique is carried out under mild reaction conditions and has a good selectivity (may higher than 95%), there are the shortages of relatively lower catalyst activity, worse catalyst stability and the like. Thus the key points of the research and development of said technique lie in preparing and modifying the corresponding catalysts so as to enhance the conversion rate of the reactions, and improving the anti-inactivation and regenerability of the catalyst.